1. Field of the Invention
The invention relates to a device and method for the aftertreatment of exhaust gases from combustion engines, and in particular for the aftertreatment of exhaust gases from internal combustion engines.
2. Description of the Related Art
In various alternative modifications, it is possible to carry out a catalytic aftertreatment and/or filtering of particles contained in the exhaust gas stream, alone or in combination.
Various possibilities are known for the exhaust-gas aftertreatment of exhaust gases from combustion engines. Additional elements, such as catalytic converters or particle filters, are arranged in an exhaust pipe, and the exhaust gases which are to be treated are passed through such elements or past them, in order to convert pollutant constituents into harmless constituents and to retain particles, in particular particulates produced during combustion in diesel engines.
For the catalytic aftertreatment of exhaust gases, it has hitherto been customary for what is known as a catalytic converter to be integrated in the exhaust pipe, the converter used being a structure which inherently has a relatively large surface area, which is increased still further by a coating which is known per se, to be doped or occupied by catalytically active materials, such as platinum, rhodium and palladium.
However, the catalytic action requires a certain minimum temperature, which with conventional systems can be reached under certain operating regimes, since in the starting phase of an internal combustion engine the required increase in temperature is only brought about by the discharge of exhaust gas. Overheating has to be avoided by the coating which has hitherto been required and increases the active surface area, since these layers, in the event of certain temperatures being exceeded, may be dissolved or flake off, and consequently a catalytic converter of this type cannot be arranged immediately after the exhaust discharge from an internal combustion engine.
A very wide range of filter systems are known to be used to filter particles, and in particular particulates, out of the exhaust gases from internal combustion engines, with both metallic and ceramic materials being used. The deposition of particulates in the known filters has hitherto made it necessary to carry out a step known as regeneration at more or less regular intervals, in order to prevent the filters from becoming substantially blocked, which would cause the dynamic pressure to build up. For regeneration of this type, it is customary to initiate combustion of the particulates which have been separated out in the filter, which requires a supply of energy, inevitably leading to a reduction in efficiency, irrespective of whether electrical heating is introduced or the required combustion is effected by the supply of combustible hydrocarbons.
The flow conditions in the exhaust-gas stream are influenced in particular by the conventional particle filters according to the loading state of the filter material, with the result that in many operating periods it is impossible to maintain optimum combustion conditions as a function of the exhaust gas back pressure.
Moreover, both production and operation of the conventional systems are expensive.